A process of manufacturing a semiconductor device may include a process of forming a thin film, such as a silicon oxide film (a SiO film), a silicon nitride film (a SiN film), or the like containing a specific element, for example, silicon (Si), on a substrate. The SiO film has good insulation properties, low permittivity, etc. such that it is widely used as an insulating film or an interlayer film. Also, the SiO film has good insulation properties, corrosion resistance, permittivity, film stress controllability, or the like such that it is widely used as an insulating film, a mask film, a charge accumulating film, or a stress control film. Also, technology that adds carbon (C) into the thin films to form a silicon carbon nitride film (a SiCN film), a silicon oxide carbon nitride film (a SiOCN film), a silicon oxide carbon film (a SiOC film), or the like is known. Carbon is added into the thin film to enhance a wet etching resistance of the thin film to hydrogen fluoride (HF). In addition, a dielectric constant or refractive index of the thin film can be altered when carbon is added into the thin film. The thin film with carbon added can be used as an optical function film having a refractive index different from that of an adjacent film.